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    <title>geom3d</title>
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    <center>Scilab Function</center>
    <div align="right">Last update : 21/12/2005</div>
    <p>
      <b>geom3d</b> - projection from 3D on 2D after a 3D
  plot</p>
    <h3>
      <font color="blue">Calling Sequence</font>
    </h3>
    <dl>
      <dd>
        <tt>[x,y]=geom3d(x1,y1,z1)</tt>
      </dd>
    </dl>
    <h3>
      <font color="blue">Parameters</font>
    </h3>
    <ul>
      <li>
        <tt>
          <b>x1,y1,z1</b>
        </tt>: real vectors of the same size (points in 3D).</li>
      <li>
        <tt>
          <b>x,y</b>
        </tt>: real vectors of the same size as <tt>
          <b>x1</b>
        </tt>,
          <tt>
          <b>y1</b>
        </tt> and <tt>
          <b>z1</b>
        </tt>.</li>
    </ul>
    <h3>
      <font color="blue">Description</font>
    </h3>
    <p>After having used a 3D plot function such as <tt>
        <b>plot3d</b>
      </tt>,
    <tt>
        <b>plot3d1</b>
      </tt> or <tt>
        <b>param3d</b>
      </tt>, <tt>
        <b>geom3d</b>
      </tt> gives
    the mapping between a point in 3D space <tt>
        <b>(x1(i),y1(i),z1(i))</b>
      </tt>
    and the corresponding point <tt>
        <b>(x(i),y(i))</b>
      </tt> in the projected 2D
    plan. Then all the 2D graphics primitives working on <tt>
        <b>(x,y)</b>
      </tt>
    can be used for superposition on the 3D plot.</p>
    <h3>
      <font color="blue">Examples</font>
    </h3>
    <pre>

deff("[z]=surf(x,y)","z=sin(x)*cos(y)")
t=%pi*(-10:10)/10;
// 3D plot of the surface
fplot3d(t,t,surf,35,45,"X@Y@Z")
// now (t,t,sin(t).*cos(t)) is a curve on the surface
// which can be drawn using geom3d and xpoly
[x,y]=geom3d(%pi/2,0,surf(%pi/2,0))
 
  </pre>
    <h3>
      <font color="blue">Author</font>
    </h3>
    <p>J.Ph.C.</p>
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